Application is made to support and publish the proceedings of the Second Conference on Matrix Vesicle Calcification. Matrix vesicles are submicroscopic, membrane-invested extracellular particles which serve as initial loci for mineralization of dentin, bone, cartilage and also non-skeletal tissues and tumors. The discovery of calcifying vesicles in cartilage was followed by a rapid series of observations and reports indicating that vesicles contain phospholipids with a strong affinity for calcium, and that their membranes are replete with phosphates which could trigger mineralization by providing a localized concentration of PO4 for formation of nascent mineral, and by hydrolysis of inhibitors of mineral growth such as pyrophosphate and ATP. Work is continuing across the world to clarify the role of vesicles in calcification. Since the time of the First Matrix Vesicle Conference in November 1974 many advances have been made including 1) new and improved systems for studying calcification by matrix vesicles in vitro; 2) further purification and characterization of matrix vesicle phosphatases; 3) the finding of calcifiable lipoproteins may be analogous to matrix vesicles in calcifying oral bacteria and in adult bone; 4) the crystallographic characterization of well preserved mineral within matrix vesicles in unfixed thin-sections; and 5) the demonstration that isolated vesicle phosphatase has calcium-accumulating properties. We feel that it is an appropriate time to organize the second Vesicle Conference to present, discuss, and summarize these new observations.